1. Field
This document relates to a parallax type stereoscopic image display device.
2. Related Art
Recently, with the increasing interest in three-dimensional stereoscopic images, there have been developed a variety of stereoscopic image display devices. Generally, a stereoscopic sense that a person perceives occurs from a complex effect of the degree of a change of thickness of the person's eye lens according to the location of an object to be observed, the angle difference of the object observed from both eyes, the differences of location and shape of the object observed from both eyes, the time difference due to a movement of the object, and other various psychological and memory effects. In particular, binocular disparity, caused by about a 6-7 cm lateral distance between the person's left eye and right eye, can be regarded as the main cause of the stereoscopic sense. Due to binocular disparity, the person perceives the object with an angle difference, which makes the left eye and the right eye receive different images, and when these two images are transmitted to the person's brain through retinas, the brain can perceive the original three-dimensional stereoscopic image by combining the two pieces of information.
Methods for displaying stereoscopic images using binocular disparity are classified into a glasses method and a non-glasses method. A glasses type stereoscopic image display device displays left and right parallax images each having a different polarization direction on a display panel, and displays a 3D image using polarization glasses or liquid crystal shutter glasses. On the other hand, a non-glasses type stereoscopic image display device includes a parallax barrier and a lenticular lens. Recently, research into these types of stereoscopic image display devices is actively under way.
As shown in FIG. 1, the parallax type stereoscopic image display spatially separates light incident from an image panel into light of a left-eye image and light of a right-eye image by using a barrier panel. The barrier panel and the image panel may be integrated into a display element. The barrier panel has a switchable barrier for selectively blocking the light incident from the image panel. As shown in FIG. 2, the switchable barrier panel comprises a liquid crystal layer LC and a first electrode pattern E1 and a second electrode pattern E2 which are formed to face each other, with the liquid crystal layer LC interposed therebetween. A driving voltage is applied to the first electrode pattern E1 to drive the liquid crystal layer LC, and a reference voltage is applied to the second electrode pattern E2. In the switchable barrier panel, when the liquid crystal layer LC is driven to block light by the driving voltage applied to the first electrode pattern E1, the liquid crystal layer LC functions as a barrier area, and when the liquid crystal layer LC is driven to cause light to pass therethrough, the liquid crystal layer LC functions as an open area.
In such a switchable barrier, the open area and the barrier area are fixed to the sizes given at design time. The size ratio between the open area and the barrier area is set to a constant value by taking viewing distance, viewing angle, etc. into account. In the parallax barrier type stereoscopic image display device, accordingly, the display quality of a 3D image varies according to viewing distance, and the viewing angle is very limited. Moreover, the concept of multi-view was introduced into the conventional parallax barrier type stereoscopic image display device to secure a viewing angle. In this case, degradation in the picture quality of stereoscopic images caused by resolution degradation is unavoidable.
Recently, a dynamic barrier technology has been introduced into the parallax barrier type stereoscopic image display device in order to compensate for viewing angle limitations and resolution degradation. The dynamic barrier technology, used in conjunction with an eye-tracking technology, is a method for compensating for a viewing angle by changing the position of the barrier as the viewer's eyes are diverted. In the dynamic barrier technology, for example, the position of the barrier is changed to the right by ΔX as shown in FIG. 3 as much as the position of the viewer's both eyes (left and right eyes) is shifted to the right from the first point P1 to the second point P2, thus securing a viewing angle enough not to cause 3D crosstalk.
To implement this dynamic barrier technology, the first electrode pattern (‘E1’ of FIG. 2) applied with the liquid crystal driving voltage needs to be finely controlled. To this end, it is inevitable to apply multiple layers (two or three layers) for multichannel configuration to the first electrode pattern. However, multilayer application may be accompanied by a luminance difference which occurs within the barrier, thereby degrading the quality of a stereoscopic image and causing visual fatigue. The main reasons for luminance difference include etch bias difference between layers, difference in effective dielectric constant, alignment tolerance, etc.